1. Field of the Present Invention
The present invention relates to a composite material in which an organic compound and inorganic compound are composited and which is superior in a carrier transporting property and a property of injecting carriers to an organic compound. Moreover, the present invention relates to a current excitation type light emitting element using the composite material. In addition, the present invention relates to a light emitting device and an electronic device having the light emitting element.
2. Description of the Related Art
In recent years, a light emitting element using an organic compound having a light emitting property has been actively researched and developed. These light emitting elements basically have a structure in which a layer including an organic compound having a light emitting property is interposed between a pair of electrodes. By applying voltage to this element, electrons and holes are injected to the layer including an organic compound having a light emitting property from the pair of electrodes, respectively, to feed current. Then, the carriers (electrons and holes) are recombined, and accordingly, an excitation state is formed by an organic compound having a light emitting property. Light is emitted when the excitation state returns to a ground state. From such a mechanism, such a light emitting element is referred to as a current excitation type light emitting element.
A singlet excitation state and a triplet excitation state can be given as types of an excitation state formed by an organic compound. Light emission from a singlet excitation state is referred to as fluorescence and light emission from a triplet excitation state is referred to as phosphorescence.
A great advantage of such a light emitting element is that such a light emitting element can be manufactured to have a thin shape and lightweight, because the light emitting element is made of an organic thin film, for example, having a thickness of approximately 0.1 μm. In addition, extremely high response speed is another advantage, because time between carrier injection and light emission is approximately 1 μsec or less. These characteristics are considered suitable for a flat panel display.
Such a light emitting element is formed in a film shape. Thus, surface emission can be easily obtained by forming a large-area element. This characteristic is difficult to be obtained by a point light source typified by an incandescent lamp or an LED or a line light source typified by a fluorescent lamp. Therefore, the above-described light emitting element also has a high utility value as a surface light source which is applicable to lighting or the like.
Meanwhile, in a display device to be incorporated into various kinds of information processing appliances which have developed rapidly in recent years, reduction of power consumption is particularly required, and it has been attempted to decrease the drive voltage of a light emitting element in order to achieve the low power consumption. Further, in view of commercialization, not only the decrease in the drive voltage but also the extension of lifetime of a light emitting element is significant. Therefore, development of a light emitting element to achieve the extension of lifetime has been advanced.
For example, in Patent Document 1 (Patent Document 1: Japanese Patent Laid-Open No. H9-63771), the decrease in a drive voltage of a light emitting element has been achieved by forming an anode with metal oxide having a high work function such as molybdenum oxide. Moreover, an advantageous effect of long lifetime is also obtained.
However, in order to extend the lifetime, a means described in Patent Document 1 is insufficient and technical development to achieve the longer lifetime has been required.